This invention relates to a process for preparing useful intermediates in the synthesis of agricultural chemicals. More, particularly, it pertains to an improved process for the selective reduction of dinitrobenzenes to the corresponding nitroanilines which may then be utilized in the synthesis of triazolinone, tetrazolinone or related herbicides.
European Patent Application 127,079, Takemoto et al. (1984), discloses a process in which 2,4-dinitrofluorobenzene is selectively reduced using between 2.5 and 4 moles of iron in the presence of acid to produce one mole of 2-fluoro-5-nitroaniline. In one example in which acetic acid was employed and the reaction mixture was refluxed for ten minutes, 2-fluoro-5-nitroaniline was produced in 70% yield, by weight. The weight % ratio of the desired 2-fluoro-5-nitroaniline to the by-product 4-fluoro-3-nitroaniline was 93:7. The use of a noble metal catalyst is not taught by this patent application.
The reduction of nitrobenzene to aniline using iron with noble metal catalysts is also known from the prior art. See, for example, Chem. Abstracts 105:26137, Ura et al. (1986); Chem. Abstracts, 98:125,604, Mitsui Chemicals (1983); Chem. Abstracts 93:94965, Seegraves (1980); Chem. Abstracts 92:146418, Cossaboon (1980); and Chem. Abstracts 83:192794, Cossaboon (1975). None of these references, however, teaches the selective reduction of dinitrobenzenes or halogenated dinitrobenzenes.
In addition, the selective reduction of dinitro aromatic compounds using palladium-catalyzed hydrogenation with triethylammonium formate has been reported by Terpko et al., J. Org. Chem., 45, 4992 (1980). No 2,4-dinitrohalobenzenes were reported as being reduced. Those compounds which were reported as having been selectively reduced include 2,2'-dinitrobiphenyl, 1,3-dinitrobenzene, and various dinitrobenzenes substituted with methyl, hydroxy, methoxy, amino, methoxycarbonyl, and methylcarbonylamino groups.